ATOMIC LAYER DEPOSITION OF GERMANIUM OR GERMANI UM OXIDE
FIELD OF THE INVENTION
The present invention relates to depositing germanium and germanium oxide with
atomic layer deposition (ALD) on substrates.
BACKGROUND OF THE INVENTION
Atomic Layer Epitaxy (ALE) method was invented by Dr. Tuomo Suntola in the early
1970's. Another generic name for the method is Atomic Layer Deposition (ALD) and
it is nowadays used instead of ALE. ALD is a special chemical deposition method
based on the sequential introduction of at least two reactive precursor species to at
least one substrate.
A basic ALD deposition cycle consists of four sequential steps: pulse A, purge A,
pulse B and purge B. Pulse A typically consists of metal precursor vapor and pulse B
of nitrogen or oxygen precursor vapor. Inactive gas, such as nitrogen or argon, and a
vacuum pump are used for purging gaseous reaction by-products and the residual
reactant molecules from the reaction space. A deposition sequence contains at least
one deposition cycle. Deposition cycles are repeated until the deposition sequence
has produced a thin film of desired thickness.
Precursor species form a chemical bond to reactive sites of the heated surfaces
through chemisorption. Reaction conditions are typically arranged in such a way that
no more than a molecular or atomic monolayer of a solid material forms on the
surfaces during one precursor pulse. Thus, the growth process is self-terminating, i.e.
saturative growth. For example, the first precursor can include ligands that remain
attached to the adsorbed species and saturate the surface, which prevents further
chemisorption. Reaction space temperature is maintained above condensation
temperatures and below thermal decomposition temperatures of the utilized
precursors such that the precursor molecule species chemisorb on the substrate(s)
essentially intact. This chemisorption step is typically followed by a first purge step
(purge A) wherein the excess first precursor and possible reaction by-products are
removed from the reaction space. Second precursor vapor is then introduced into the
reaction space. Second precursor molecules typically react with the adsorbed
species of the first precursor molecules, thereby forming the desired thin film
material. This growth terminates once the entire amount of the adsorbed first
precursor has been consumed. The excess of second precursor vapor and possible
reaction by-product vapors are then removed by a second purge step (purge B). The
cycle is then repeated until the film has grown to a desired thickness.
Germanium is a promising material for use in semiconductor and optoelectronic
devices because it has very high mobility and generally very good transport
properties. Compared to silicon or gallium, germanium is much more ordered and
has better mobility, making it useful e.g. as a gate oxide in silicon or germanium
based transistors.
Despite the great interest of e.g. the semiconductor industry in Ge-deposition, ALD
processes for depositing germanium have not been successful. Thus, there still
remains a need for industrially applicable methods for depositing germanium and
germanium oxide layers on various substrates.
SUMMARY
According to a first aspect of the invention there is provided a process of depositing
germanium on a substrate, comprising sequentially exposing in at least one
deposition cycle the substrate inside a chamber with a Ge-containing precursor and a
reducing or oxidizing precursor.
According to certain example embodiments the invention provides a method of
depositing elemental germanium (Ge) or germanium dioxide (GeC>2) on substrates,
the deposition method comprising sequentially exposing in at least one deposition
cycle a substrate inside a deposition chamber with germanium precursor and
reducing or oxidizing gas, respectively.
In certain example embodiments the sequential exposure of the substrate comprises
running a deposition sequence comprising at least one deposition cycle of Ge
precursor pulse; a purge with an inert gas; reducing or oxidizing pulse; and a purge
with an inert gas. Accordingly, in certain example embodiments, said at least one
deposition cycle comprises:
a. Ge-containing precursor pulse;
b. Purge with an inert gas;
c . Reducing or oxidizing pulse; and
d. Purge with an inert gas.
In certain example embodiments, in step c the reducing precursor is selected from
the group consisting of H 2 and hydrogen plasma.
In certain example embodiments, H2 is used in step c of the deposition cycle as the
reducing pulse in an amount of about 4-100%, preferably about 5-50%, most
preferably about 15 % (volume/volume) in a mixture with an inert gas.
In certain example embodiments, in step c the oxidizing precursor is selected from
0 2, 0 3, H20 2, oxygen plasma, water and water plasma.
The sequential self-saturating surface reactions in ALD produce the desired coating
on the substrate inside the deposition chamber. Accordingly, in certain example
embodiments, the substrate is coated by using ALD so that essentially all surfaces of
the substrate are exposed to the reactants and coated.
The process according to the invention for depositing substrates with germanium or
germanium oxide can be carried out with the apparatus described in WO
2009/144371 .
According to a second aspect of the invention there is provided use of
tetrakis(dimethylamino)Ge in atomic layer deposition.
In certain example embodiments, said atomic layer deposition is for depositing a
silicon substrate.
According to a third aspect of the invention there is provided a Ge deposited article
manufactured by coating an undeposited article as a substrate by the process
according to the first aspect or its embodiments.
Different non-binding example aspects and embodiments of the present invention
have been illustrated above. The above embodiments are used merely to explain
selected aspects or steps that may be utilized in implementations of the present
invention. Some embodiments may be presented only with reference to certain
example aspects of the invention. It should be appreciated that corresponding
embodiments may apply to other example aspects as well. Any appropriate
combinations of the embodiments may be formed.
Accordingly, the following detailed description is not to be taken in a limiting sense,
and the scope of the present invention is defined only by the appended claims.
BRIEF DESCRIPTION OF THE FIGURES
Fig. 1 is an XRD graph providing data on deposition using the deposition method
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following description, Atomic Layer Deposition (ALD) technology is used to
make Ge or Ge0 2 coatings on substrates. The basic principles of the ALD deposition
are known to a skilled person. As discussed above, ALD is a special chemical
deposition method based on the sequential introduction of at least two reactive
precursor species to at least one substrate. The method according to the invention is
equally applicable to coating more than one substrate of same or different type. The
at least one substrate is exposed to temporally separated precursor pulses in a
reaction chamber to deposit material on the substrate surfaces by sequential selfsaturating
surface reactions. In the context of this application, the term ALD
comprises all applicable ALD based techniques and any equivalent or closely related
technologies, such as, for example MLD (Molecular Layer Deposition) technique.
A basic ALD deposition cycle consists of four sequential steps: pulse A, purge A ,
pulse B and purge B. Pulse A consists of a first precursor vapor and pulse B of
another precursor vapor. Inactive gas and a vacuum pump are typically used for
purging gaseous reaction by-products and the residual reactant molecules from the
reaction space during purge A and purge B. A deposition sequence comprises at
least one deposition cycle. Deposition cycles are repeated until the deposition
sequence has produced a thin film or coating of desired thickness.
The ALD process according to certain example embodiments is further illustrated by
the following description. Ge or GeC>2 is grown on a substrate from heated Ge
precursor and reducing/oxidizing precursor. A heated Ge precursor source is heated
to a selected source temperature to create sufficient Ge precursor vapor pressure to
be transferrable to the reaction chamber at about 0.1-10 Torr. In some embodiments
which use heat-sensitive precursors or substrates it is advantageous to evaporate
the precursor at temperatures as low as possible to avoid unnecessary
decomposition of precursors or substrates, while still generating a sufficiently big
precursor vapor dosage for covering the whole substrate surface. A skilled person is
able to adjust the required temperature according to the particular precursor and
substrate.
An advantage of volatile precursors at low pressure is that low pressure increases
the diffusion speed of gas molecules and helps to recover the equilibrium vapor
pressure as fast as possible.
In certain example embodiments, the first precursor is selected from the group
consisting of tetrakis(dimethylamino)Ge and derivatives of germanium amidinates,
alkyl germanium; alky halide germanium; tetramethyl-Ge, (CHs^GeCI; germanium
beta-diketonates, germanium acetyl acetonates, and germanium halides. The second
precursor is selected from the group consisting of H2, hydrogen plasma, and 0 2, 0 3,
H2O2, oxygen plasma, water and water plasma.
5 In certain example embodiments, tetrakis(dimethylamino)Ge, having the chemical
formula [(CH3)2N] Ge, is used in the atomic layer deposition method.
In certain example embodiments, tetrakis(dimethylamino)Ge is used as the first
precursor and the second precursor is O3. The following deposition reaction is
10 obtained:
[(CH3)2N]4Ge + 0 3 - Ge0 2 + by products
In certain example embodiments, tetrakis(dimethylamino)Ge, having the chemical
15 formula [(CH3)2N] Ge, is used as the first precursor and the second precursor is H2.
The following deposition reaction is obtained:
[(CH3)2N]4Ge + H* - Ge + by products
20
H* refers to radicals, plasma and other energetic species.
The amount of hydrogen as the second precursor in the process may vary. Suitable
amounts of H2 in this respect are 4%-1 00% based on the volume of hydrogen in an
25 inert carrier gas. The amount of H2 may be about 4%-90%, about 4%-80%, about
4%-70%, about 4%-60%, about 4%-50%, about 4%-40%, about 4%-30%, about 4%-
20%, about 4%-10%, about 10%-90%, about 10%-80%, about 10%-70%, about
10%-60%, about 10%-50%, about 10%-40%, about 10%-30%, or about 10-20%,
such as about 95%, 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%,
30 35%, 30%, 25%, 20%, 15%, 10%, 5% or 4%. Suitably, the inert carrier gas may be
N2 or Ar. When hydrogen plasma is used, the inert gas is preferably Ar.
The formation of the deposited layer can be verified e.g. by X-ray diffractometry
(XRD), X-ray photon spectroscopy (XPS), or X-ray reflection (XRR).
The deposition process may be carried out at a temperature in the range of about
5 300°C - about 800°C, such as at about 800°C, 750°C, 700°C, 650°C, 600°C, 550°C,
500°C, 450°C, 440°C, 430°C, 420°C, 410°C, 400°C, 390°C, 380°C, 370°C, 360°C,
350°C, 340°C, 330°C, 320°C, 3 10 or 300°C. Suitably lower temperatures are
preferred in which the risk of decomposing the precursor is lower.
0 The following embodiments are provided:
Embodiment 1. A process of depositing germanium on a substrate comprising
sequentially exposing in at least one deposition cycle the substrate inside a chamber
with a Ge-containing precursor and a reducing or oxidizing precursor.
5
Embodiment 2. The process according to embodiment 1, wherein the at least one
deposition cycle comprises:
a . Ge containing precursor pulse;
b. Purge with an inert gas;
0 c . Reducing or oxidizing pulse; and
d . Purge with an inert gas.
Embodiment 3. The process according to embodiment 1 or 2, wherein in step c the
reducing precursor is selected from the group consisting of H2 and hydrogen plasma.
5
Embodiment 4. The process according to any one of embodiments 1-3, wherein H2 is
used in the step c of the deposition cycle as the reducing pulse in an amount of about
4-100%, preferably about 5-50%, most preferably about 15 % (volume/volume) in a
mixture with an inert gas.
0
Embodiment 5. The process according to embodiment 1 or 2, wherein in the step c
the oxidizing precursor is selected from O2, O3, H2O2, oxygen plasma, water and
water plasma.
Embodiment 6. The process according to any one of embodiments 1-5, wherein the
deposition cycle is carried out at a temperature of about 50°C - about 800°C,
preferably at about 100°C - about 500°C, more preferably at about 300°C - about
400°C, most preferably at about 350°C.
Embodiment 7. The process according to any one of embodiments 1-6, wherein the
inert gas is nitrogen or argon, and the inert gas is argon when a plasma precursor is
used.
Embodiment 8. The process according to any one of embodiments 1-7, wherein the
Ge-containing precursor has a volatility of at least 1 hPa at temperature a range of
from room temperature to 200°C.
Embodiment 9. The process according to any one of embodiments 1-8, wherein the
Ge-containing precursor is selected from the group consisting of alkyl germanium,
alkylamine germanium, tetrakis(dimethylamine) germanium, diketonate germanium,
germanium halides, and germanium alchoxide.
Embodiment 10. The process according to any one of embodiments 1-9, wherein the
substrate is a silicon substrate, germanium substrate, lll-V semiconductor, silicon
oxide, or germanium oxide substrate, or a substrate based on inorganic and
organic/polymer materials.
Embodiment 11. The process according to any one of embodiments 1-10, wherein
the process is based on self-saturating surface reactions.
Embodiment 12. The process according to any one of embodiments 1-1 1, wherein
the deposition cycle is repeated until the deposited layer has a thickness of 10-1 00
nm.
Embodiment 13. Use of tetrakis(dimethylamino)Ge in atomic layer deposition.
Embodiment 14. The use according to embodiment 13, wherein said atomic layer
deposition is for depositing a silicon substrate.
Embodiment 15. The use according to any one of embodiments 13-14 wherein the
use comprises depositing Ge or GeC>2.
Embodiment 16. A Ge or Ge0 2 deposited article manufactured by coating an
undeposited article as a substrate by the process according to any one of
embodiments 1-12.
EXAMPLES
The following examples are provided to illustrate various aspects of the present
invention. They are not intended to limit the invention, which is defined by the
accompanying claims.
Example 1 - Deposition of elemental germanium
Tetrakis(dimethylamino)germanium and H2 were used as precursors to deposit Ge
on Si substrate.
The following deposition cycle at 350°C was used to run 1000 cycles. Suitable line
pressure for precursor source line is 1-1 0 torr, reaction vessel pressure 1-10 torr,
inert carrier gas flow rate 30-300 seem:
1s [(CH 3)2N]4Ge / 2s N2 / s 5% H2 in N2 / 1s N2
As revealed by the XRD analysis shown in Fig 1, Ge film was deposited on the Si
substrate. The small amount of Ge oxide seen in the analysis is due to oxidation of
the deposited Ge layer caused by oxygen present in the atmosphere.
Instead of tetrakis(dimethylamino)Ge, one or more of the following Ge-containing
precursors may be used to deposit Ge or Ge0 2 on substrates: alkyl germanium; alky
halide germanium; alkyl germanium; alkyl halide germanium; tetramethyl-Ge,
(CH3)3GeCI; germanium beta-deketonates; germanium acetyl acetonates: and
germanium amidinates. Suitably, the deposition parameters, such as temperature
and, reaction pressure, precursor line pressure are adjusted to be compatible with
the particular precursor.
The above deposition method can also be carried out at various temperatures listed
above as long as the temperature is below decomposition temperature of the
precursors.
Example 2 - Deposition of germanium dioxide
Tetrakis(dimethylamino)germanium and 0 3 were used as precursors to deposit Ge0 2
on a Si substrate.
The following deposition cycle at 350°C was used to run 1000 cycles:
1s [(CH3)2N]4Ge / 2s N2 / s 0 3 / 1s N2
The substrate was coated with a Ge oxide film.
Instead of tetrakis(dimethylamino)Ge one or more of the following Ge-containing
precursors may be used: alkyl germanium; alky halide germanium; alkyl germanium;
alkyl halide germanium; tetramethyl-Ge, (CH3)3GeCI; germanium beta-diketonates;
germanium acetyl acetonates: and germanium amidinates.
The above deposition method can also be carried out at various temperatures below
decomposition temperature of the precursors.
Claims
1. A process of depositing germanium on a substrate comprising sequentially
exposing in at least one deposition cycle the substrate inside a chamber with a
Ge-containing precursor and a reducing or oxidizing precursor.
2. The process according to claim 1, wherein the at least one deposition cycle
comprises:
a . Ge containing precursor pulse;
b. Purge with an inert gas;
c . Reducing or oxidizing pulse; and
d . Purge with an inert gas.
3. The process according to claim 1 or 2, wherein in step c . the reducing
precursor is selected from the group consisting of H2 and hydrogen plasma.
4. The process according to any one of claims 1-3, wherein H2 is used in the step
c . of the deposition cycle as the reducing pulse in an amount of about 4-100%
(vol./vol.), preferably about 5-50% (vol./vol.), most preferably about 15 %
(vol./vol.) in a mixture with an inert gas.
5. The process according to claim 1 or 2, wherein in the step c . the oxidizing
precursor is selected from 0 2, 0 3, H20 2, oxygen plasma, water and water
plasma.
6. The process according to any one of claims 1-5, wherein the deposition cycle
is carried out at a temperature of about 50°C - about 800°C, preferably at
about 100°C - about 500°C, more preferably at about 300°C - about 400°C,
and most preferably at about 350°C.
7. The process according to any one of claims 1-6, wherein the inert gas is
nitrogen or argon, and the inert gas is argon when a plasma precursor is used.
8. The process according to any one claims 1-7, wherein the Ge-containing
precursor has a volatility of at least 1 hPa at a temperature range of from room
temperature to 200°C.
9. The process according to any one of claims 1-8, wherein the Ge-containing
precursor is selected from the group consisting of alkyl germanium, alkylamine
germanium, tetrakis(dimethylamine) germanium, diketonate germanium,
germanium halides, and germanium alchoxide.
10. The process according to any one of claims 1-9, wherein the substrate is a
silicon substrate, germanium substrate, lll-V semiconductor, silicon oxide, or
germanium oxide substrate, or a substrate based on inorganic and
organic/polymer materials.
11. The process according to any one of claims 1-10, wherein the process is
based on self-saturating surface reactions.
12. The process according to any one of claims 1- 11, wherein the deposition cycle
is repeated until the deposited layer has a thickness of 10-1 00 nm.
13. Use of tetrakis(dimethylamino) germanium in atomic layer deposition.
14. The use according to claim 13, wherein said atomic layer deposition is for
depositing a silicon substrate.
15. A Ge deposited article manufactured by coating an undeposited article as a
substrate by the process according to any one of claims 1-12.